The Jet Stream and Recent Flooding

What’s with the weird weather this month? In case you missed it, McGrath, Alaska, hit 94 degrees on June 17, four degrees warmer than Miami, which sits 4200 miles closer to the equator. On that same day, 1750 miles to the southeast of McGrath in Calgary, Canada, the high temperature barely hit 70. But Calgary and the surrounding area were in the midst of massive downpours and flooding that swamped the city and forced the evacuation of 75,000 people. Meanwhile, on the other side of the Atlantic, parts of Europe have also been coping with extreme flooding. And it’s all part of the same strange weather phenomenon.

“It’s the jet stream,” says John Nielsen-Gammon, a professor of atmospheric science at Texas A&M University. “Actually, it’s due to two jet streams in the Northern Hemisphere when there’s normally just one. It’s something that we see once a decade or so during this time of year.”

4 Responses

Hmmm. You deny a connection to climate change, yet I thought it was increasingly the subject of papers suggesting that it could indeed be related to less ice in the Arctic, which I don’t think anyone doubts is a result of AGW? Or am I confusing discussion of “blocking events” as something separate from jet stream movement?

I know the question is not resolved, but a simple denial of connection seems hardly wise either.

What I told the reporter was that I didn’t know of any direct connection to climate change, other than increased moisture. I haven’t seen any papers on this subject for this season. What I’ve seen involves fall sea ice possibly affecting winter jet structure, and fall sea ice anomalies are 3-4 times as large as spring sea ice anomalies.

Very interesting, although averaging the jet over a long period loses the variability, which can be seen here. It could be my own lack of understanding, but based on the animation it appears that what we’re seeing now is the main jet tending to send branches poleward, which in turn don’t seem to persist long. IOW the polar ring shown in the averaging graphic isn’t very apparent at any one time. But perhaps this is a distinction without much meaning.

Can you point to any research on this phenomenon, John? I tried a keyword search in Google Scholar but wasn’t able to narrow things down enough to find anything relevant.

Re the question of whether or not this could be AGW-related, an inherent problem is that any AGW-induced circulation change can be instead described in terms of synoptic factors, albeit that the hammer and anvil of tropical expansion and polar amplification are clear enough.

Re the sea ice loss-jet connection, there does seem to be a pretty active argument as to whether it’s really the sea ice as such or polar amplification more generally (see e.g. recent work from Screen and Simmonds). Of course it’s complicated since even if it’s the latter sea ice loss will have a feedback role in the larger picture. In any event, if it is polar amplification more broadly then it becomes possible to consider that effects on the jet may be occurring in other seasons.

Finally, John, re the current situation, how unusual is the current massive ridge we’re seeing in the west? Is there thought to be a particular association with the split jet?

Steve – Sorry, I’m traveling, so can’t respond in detail. For further info, try Jupiter. There’s been a lot of work on why particular planets should have a certain number of jets. For Earth, the proper number per hemisphere seems to be about 1.5, which makes things a lot more interesting than 1 or 2. – John